Final answer:
The presence of NaSO4 as a contaminant in NaGPOx·12H2O would decrease the yield of Ba3(PO4)2 due to the common ion effect and the potential formation of an insoluble compound, BaSO4.
Step-by-step explanation:
If NaSO4 is an unknown contaminant of NaGPOx·12H2O, its presence would affect the yield of Ba3(PO4)2 negatively, specifically it would cause the yield to decrease. The contamination by NaSO4 would contribute sulfate ions (SO42−) which do not react to form barium phosphate, the desired product. Instead, these extra ions could potentially precipitate with barium ions (Ba2+) to form barium sulfate (BaSO4), which is highly insoluble and would be an additional product. This would reduce the concentration of barium ions available to react with phosphate ions to form barium phosphate, thus decreasing the yield of Ba3(PO4)2. According to the principles of chemical equilibria, the presence of additional ions from contaminants such as NaSO4 can shift the equilibrium, a concept known as the common ion effect, thereby affecting the solubility and subsequent yield of the intended product.